Abstract
Electrochromic devices can act as passive displays. They change their color when a low voltage is applied. Flexible and bendable hybrid textile-film electrochromic devices with poly-3,4-ethylenedioxythiophene polystyrene sulfonate (PEDOT:PSS) were prepared on polyethylene polyethylene terephthalate (PEPES) membranes using a spray coating technique. The electrolyte consisted of a gelatin glycerol mixture as host matrix and calcium chloride. Titanium dioxide was used as an ion storage layer and a carbon containing dispersion was used for the counter electrode on a polyester rip-stop fabric. The sheet resistance of PEDOT:PSS on PEPES was 500 Ohm/sq. A 5 × 5 electrochromic matrix with individually addressable pixels was successfully designed and assembled. The switching time of the pixels was 2 s at a voltage of 2.0 V directly after assembling. The use of titanium dioxide as ion storage also increased the contrast of the dark-blue reduced electrochromic layer. Coloration was not self-sustaining. The PEDOT:PSS layer needed a constant low voltage of at least 0.5 V to sustain in the dark-blue reduced state. The switching time increased with time. After 12 months the switching time was ~4 s at a voltage of 2.8 V. The addition of glycerol into the electrolyte extended the lifetime of a non-encapsulated textile electrochromic cell, because moisture is retained in the electrolyte. Charge carriers can be transported into and out of the electrochromic layer.
Highlights
Reversible color changing materials can be grouped according to the external stimulus, which induces the color change
The successful fabrication of a textile integrated ECD with individually addressable pixels for the controllable ability to change the display of patterns and coloration is demonstrated
A moisture-retaining agent in the electrolyte ensures that the electrolyte does not dry out and the and miniaturization of the pixel matrix allow a flexible display for information or camouflage electrochromic cell retains its functionality
Summary
Reversible color changing materials can be grouped according to the external stimulus, which induces the color change. Hydrochromic materials react to the presence of water or water vapor, thermochromic materials react to the change of temperature, mechanochromic materials to mechanical stress, photochromic materials to illumination, and electrochromic materials to a voltage [1,2,3,4]. Electrochromic materials have been considered for decades. Color changing materials can be used as decorative elements, but they can act as actuators. Electrochromic materials change their color reversibly depending on their current redox state. Prominent examples are electrochromic windows for buildings and rear-view mirrors in automotive applications [5]
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